engine whistle when cold...

when it is cold outside...say below 20 degrees...i sometimes hear a whistle coming from under the hood until the engine warms up. it isn't a constant whistle but seems to come and go as the engine goes through different revs. i'd heard the noise a few times last year but we had a pretty mild winter and really didn't pay much attention to it given it only occurred a couple times. this year i've also heard is several times. i don't think it's the accessory drivebelt squealing cause i know what that sounds like. to me it almost sounds like a vacuum leak of some sort....any ideas out there on what this could be??

I don't know what is making the noise, but mine does it too. I recently traded my 01 Screw 5.4 for the same truck in an 03. Love the truck, runs and shifts much better than my 01. I have only rolled 800 miles so far and this is the only mystery noise I have to date. My 01 had the clunk, the intermitted cold start thing and a couple other little things that I never bothered to take it to the dealer for. Noticed it within the first 200 miles. Mine does it when temps are below 50F and goes away quickly. I agree it sounds like a vacuum leak, but I don't think thats what it is. Since performance and mileage are better than expected and everything else seems to be working, I am not too worried about this deal yet, but I am curious as to what the cause is. If it were some kind of vacuum leak would'nt it make the noise all the time? Not being a smart___, just thinking outloud, I am not a mechanic, but do most of my own maintenance and repairs, and kinda enjoy troubleshooting these type of things. Although, I wish just once I could buy a new truck and not have issues with it within the first 200 miles.
By the way I am new to the board, but have been reading and enjoying ya'lls company for a while.

Here is some more information on that particular tsb. I own a service shop and subscribe to all data. They receive tsb's from the manufacturers. The only thing that did not copy we're a couple of photographs. That tube is off of the intake and shaped a little like a "U". A boot is on the back of the hose. From the front of your vehicle, trace the air cleaner element back to the intake and you will see the hose. The back attaches to the intake.

Some vehicles equipped with the 5.4L 2V engine may exhibit a "whistling" noise from the formed nylon tube in the idle-air bypass flow circuit. This may be caused by air flow passing through the sharp bend radius of the original tube assembly.

ACTION

Remove and replace formed nylon tube with the Nipple And Hose Assembly 2L1Z-9W548-AA. This action will correct the sharp bend in the tube. Refer to the following Service Procedure for details.

SERVICE PROCEDURE

1. Remove the formed tube as shown (Figure 1).

2. Replace with Nipple And Hose Assembly with part 2L1Z-9W548-AA.

3. Connect nipple to the air-inlet zip tube and the free end connects to resonator as shown (Figure 2).

4. Ensure that there are no kinks in the rubber hose which could restrict air flow.

LABOR OPERATION CLAIMING CHART

PARTS BLOCK

OTHER APPLICABLE ARTICLES: NONE

WARRANTY STATUS:
Eligible Under The Provisions Of Bumper To Bumper Warranty Coverage And Emissions Warranty Coverage

I've heard a whistle under similar circumstances (always cold weather and cold engine), but to clarify further I'm usually at light part throttle and in the process of slightly decreasing throttle angle when it occurs. I think every F150 I've owned has made this noise, so it doesn't bother me. I have always speculated that it was due to the density of the cold air whistling past some unpolished/unchamfered passages within the throttle body. (The reason I think that is because back when I had an LT1 camaro, the cheap BBK throttle bodies would make a similar whistle until you went in with a dremel and cleaned up some of the sharp edges.)

Funny what this community does, eh? Makes us think/ponder about things that we probably wouldn't ordinarily spend a single brain cycle on.

OK, now I am pissed! Had the truck at the dealer yesterday for the whistling noise at startup when it is cold. They claimed they heard something, but that everything was normal. I am starting to wonder if dealers even check TSB's when you take your vehicle in with a problem. They could have spent two minutes looking it up and had it fixed. Now they are going to have to explain to me why I am in there for the same issue for the second time.

I own a Volvo and Honda speciality repair shop. One of the tools that we have is "All Data." It allows us to not only have access to manufacturer's technical manuals, but also to tsb's from all the car companies.

If you need any more info I will try to pull relevant tsb's for you guys.

In the meantime, I am headed to detroit next month for the auto show. I really have my eyes on a 2004 150, so we will see how she looks.

Well the dealer is finally doing something good. They are going to order the parts for me without me bringing the truck back in for them to hear the whistle. They will not however admit that they messed up. The service rep I am dealing with said the tech did not hear a whislte, yet their report said they did and it was normal. Bottom line is it should be fixed once the parts come in. Thanks to troyk and titank for the info on the TSB.

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